An estimated 153,100 new cases of cancer and 70,400 deaths from cancer will occur in Canada in 2006. Men outnumber women for both new cases and deaths, by 5% for incidence and 11% for mortality. Three types of cancer account for at least 55% of new cases in each sex: prostate, lung, and colorectal cancers in males, and breast, lung, and colorectal cancers in females. Twenty nine percent of cancer deaths in men and 26% in women are due to lung cancer alone. On the basis of current incidence rates, 38% of Canadian women and 44% of men will develop cancer during their lifetimes. On the basis of current mortality rates, 24% of women and 29% of men, or approximately 1 out of every 4 Canadians, will die from cancer (Canadian cancer society, 2006).
Over the past two decades the Division of Cancer Prevention of the US National Cancer Institute has organized a research and development program for the clinical evaluation of potential cancer preventive agents. The NCI define chemoprevention as an innovative area of cancer research that focuses on the prevention of cancer through pharmacologic, biologic, and nutritional interventions. As originally described, this involves the primary prevention of initiation and the secondary prevention, delay, or reversal of promotion and progression (Crowell J. A., and al., European Journal of Cancer 41, 2005).
Epidemiological studies have shown a correlation between high fat consumption and an increased risk of breast cancer (Wynder E L, Cancer, 58, 1986). In addition, both the type and amount of dietary fat appear to affect development of breast cancer (Bartsch H, and al. Carcinogenesis 20, 1999). A relatively high intake of n-6 polyunsaturated fatty acids (PUFAs) is considered to be a risk factor and is associated with a more advanced stage of the disease at the time of diagnosis (Nomura A M, and al., Breast Cancer Res Treat 18, 1991) and reduced survival (Rohan T E, and al., Nutr Cancer, 20, 1993). In contrast, an inverse relationship exists between the incidence of breast cancer and the level of fish consumption, suggesting a protective role for n-3 PUFAs in human breast cancer.
A diet containing LA (n-6 PUFA) stimulated the growth and metastasis of human breast cancer cells transplanted into athymic nude mice, whereas EPA or DHA exerted suppressive effects compared with palmitic acid (PA). Thus, in agreement with the epidemiological observations, LA (n-6 PUFA) accelerates, whereas EPA and DHA (n-3 PUFA) suppress mammary cancer compared with PA diet in experimental systems (Rose D P, and al., JNCI 87, 1995) (Senzaki H, and al., Anticancer Res 18, 1998).